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The bowl-shaped trace fossil Piscichnus waitemata Gregory 1991 appears in Pliocene sandstones from Santa Maria Island (Azores Archipelago), extensively excavated during a stage of island evolution when the volcanic edifice was a guyot (flat-topped seamount) isolated in the NE Atlantic. The host sediments were deposited at depths from the intertidal zone to fair-weather wave base in a tropical climate under the influence of periodic storms and hurricanes. The traces were produced by ray fishes hunting for polychaetes, crustaceans and bivalves living in the sediment, similar to present-day nearshore, warm waters in the Azores, Baja California Sur (Mexico), and New Zealand, from which examples of feeding depressions are drawn (incipient Piscichnus). While P. waitemata is abundantly present in planar sediments on top of the guyot, far fewer trace fossils occur in sandstone deposited on the guyot's margins. Presumably, the different densities of ray holes in the two sedimentary bodies were a response to lesser availability of prey, lower seawater temperatures (due to greater depths), and a more dynamic environment in which life conditions were less favorable. Moreover, the potential preservation of bowl-shaped depressions was lower in this setting, given the steepness of the seafloor, stronger currents, and constant sediment mobility. The top of the guyot was a more favorable habitat, refuge and/or nursery ground for many ray fishes. Measurement of the diameters of the ray holes indicate three distinct size classes, which may suggest that several species were responsible for their formation.

Located at the interface between land and sea, marl prairies are sensitive to changes in water balance and useful recorders of climate and sea-level changes. Palustrine carbonate in marl prairies precipitates in temporary, barely flooded grasslands within microbial mats. Despite the special mode of carbonate production, descriptions of the sedimentary facies are exceptional and cursory because marl prairies are so far reported only from the recent of the Everglades (Florida, USA), where they produce an unspectacular calcite mud. We present a Pleistocene Everglades-type marl prairie from coastal Tanzania as the first fossil example. The unique preservation and high productivity (two times higher than in the Everglades) of the periphyton community in this marl prairie is due to increased calcification of coccoid and filamentous cyanobacteria. The excellent preservation allows us to characterize a marl prairie facies in great detail for the first time. Facies analyses of the sediments reveal a transition from tidal to terrestrial settings that started at ca. 44 14 C ka in response to eustatic sea-level fall and coastal tectonic uplift. The resultant drop of the groundwater table triggered the development of the marl prairie. The decline of the marl prairie was initiated at ca. 33 14 C ka due to the onset of the Last Glacial Aridity Maximum in equatorial East Africa.